The present invention is directed to a method for producing a relief surface structure on a surface of a substrate by utilizing an erosion or removing process.
Surface structures that are microscopically relief-like, for example three-dimensionally structured, are applied in many technical areas. Examples are in integrated optics to form optical layer-thickness tapers in optical waveguides, geodetic lenses or integrated microlenses. Another area is optical interconnects, for example, to form Fresnel lenses and to form integrated opto-electronics which, for example, have the form of flat transitions for optical waveguides between structural levels. The relief structure is also used in optical grating technology to form a blaze grating and the structure is used to form micromechanics.
Various methods were previously proposed or utilized for producing such three-dimensional structured surface structures. These include:
a) Sputtering on a structured etching mask in a shadow-casting technique and subsequently etching in a process that erodes both the mask as well as the material. There are difficulties in this method in view of the alignment or adjustment possibilities and in the influenceability of the taper form.
b) The multiple repetition of the process sequence of "lithography and etching". For example, this method can be employed for the manufacturing of a Fresnel lens or integrated microlenses, but is extremely time-intensive and only allows an extremely rough thickness graduation. Moreover, adjustment and alignment problems will occur.
c) Etching with an etching mask of a photoresist that was vertically rounded off by a hard bake. This method, for example, can be applied for the manufacturing of microlenses, but presents difficulties in view of the limited control of the vertical form due, for example, to boundary angles at the resist edge.